[example] Add ETL examples with assertion

Co-authored-by: Raphael Lehmann <raphael@rleh.de>

examples/generic/etl/main.cpp

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+/*
+ * Copyright (c) 2021, Raphael Lehmann
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <modm/board.hpp>
+#include <etl/unordered_map.h>
+#include <numbers>
+
+using namespace std::chrono_literals;
+
+int main()
+{
+	Board::initialize();
+
+	while (true)
+	{
+		// Create an unordered_map of three strings (that map to strings)
+		etl::unordered_map<uint8_t, double, 3> u = {
+			{15, std::numbers::pi},
+			{42, std::numbers::e},
+			{87, std::numbers::sqrt2}
+		};
+
+		if (Board::Button::read()) {
+			// Access non-existant element causing an assertion
+			MODM_LOG_INFO << u[12];
+		}
+
+		MODM_LOG_INFO << "Iterate and print keys and values using structured binding (since C++17):\n";
+		for( const auto& [key, value] : u ) {
+			MODM_LOG_INFO << "Key:[" << key << "] Value:[" << value << "]\n";
+		}
+
+		modm::delay(5000ms);
+	}
+
+	return 0;
+}

examples/generic/etl/project.xml

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+<library>
+  <extends>modm:nucleo-f439zi</extends>
+  <options>
+    <option name="modm:build:build.path">../../../build/generic/etl</option>
+  </options>
+  <modules>
+    <module>modm:etl</module>
+    <module>modm:build:scons</module>
+  </modules>
+</library>

examples/linux/etl/main.cpp

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+/*
+ * Copyright (c) 2021, Raphael Lehmann
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <etl/unordered_map.h>
+#include <numbers>
+#include <chrono>
+#include <modm/debug/logger.hpp>
+
+using namespace std::chrono_literals;
+
+int main()
+{
+	// Create an unordered_map of three strings (that map to strings)
+	etl::unordered_map<uint8_t, double, 3> u = {
+		{15, std::numbers::pi},
+		{42, std::numbers::e},
+		{87, std::numbers::sqrt2}
+	};
+
+	MODM_LOG_INFO << "Iterate and print keys and values using structured binding (since C++17):\n";
+	for( const auto& [key, value] : u ) {
+		MODM_LOG_INFO << "Key:[" << key << "] Value:[" << value << "]\n";
+	}
+
+	// Access non-existant element causing an assertion
+	MODM_LOG_INFO << u[12];
+
+	return 0;
+}

examples/linux/etl/project.xml

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+<library>
+  <!-- CI: run fail -->
+  <options>
+    <option name="modm:target">hosted-linux</option>
+    <option name="modm:build:build.path">../../../build/linux/etl</option>
+  </options>
+  <modules>
+    <module>modm:etl</module>
+    <module>modm:debug</module>
+    <module>modm:platform:core</module>
+    <module>modm:build:scons</module>
+  </modules>
+</library>